Archaeologist John Janusek, at left, and a local guide inspect a roughly carved andesite block near the shore of Lake Titicaca in Bolivia. The building blocks for Tiwanakus great temples, such huge stones were quarried 40 miles (64 kilometers) away near Copacabana, floated on reed rafts to this landing site, and then pulled ten miles (16 kilometers) to Tiwanaku. Andesite has ritual significance because its associated with Copacabana and Lake Titicaca, says Janusek. The precision of construction and the use of large blocks was a way of impressing Tiwanaku pilgrims.